It is conventional in gas chromatography to position the chromatographic column within an oven which is then programmed through a preselected temperature cycle to assist in the elution of components from a sample. The ovens of such systems commonly include fans which function to maintain even heat distribution and expedite cooling during portions of the temperature cycle.
In a conventional chromatographic oven, the fan speed remains essentially constant. However, the oven enclosure includes inlet and outlet vents which are adjusted mechanically, such as by means of solenoid actuators, stepping motors, or other separately energized mechanical devices. An example of one such arrangement is disclosed in U.S. Pat. No. 4,111,643 of Welland. If the need for such controls could be avoided, it will be apparent that a lower cost system would be feasible.
Another disadvantage of prior art controls is that the full range of air circulation volume is controlled by the size of the inlet and outlet air openings. This is because the fixed speed of the fan establishes an upper limit on the volumetric air flow rate. Therefore, increasing the area of the openings does not necessarily result in a proportional increase in air flow.